Method of multiple coating



p 4, 1956 T. A. RUSSELL 2,761,791

METHOD OF MULTIPLE COATING Filed Feb. 25, 1955 4 Sheets-Sheet 1 IN V EN TOR.

Arroawzw p 4, 1956 T. A. RUSSELL 2,761,791

METHOD OF MULTIPLE COATING Filed Feb. 25, 1955 4 Sheets-Sheet 2 Sept. 4, 1956 T. A. RUSSELL 2,751,791

METHOD OF MULTIPLE COATING Filed Feb. 23, 1955 4 Sheets-Sheet 5 my/k/p' @h u 1 1 H' @mmmmm:mummn b TheodomARussell I 5?, 08 fiNZNTOR.

F1910 p BY M I Z I ATTORNEZY p 4, 1956 T. A. RUSSELL 2,761,791

METHOD OF MULTIPLE COATING Filed Feb. 23, 1955 4 Sheets-Sheet 4 neodofeARassell 0g? .EVZNTOR.

M BY 2 1 ATTORNEYS United States Patent ()fice 2,761,791 Patented Sept. 4, 1956 METHOD OF MULTIPLE COATING Theodore A. Russell, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application February 23, 1955, Serial N 0. 489,863

14 Claims. (Cl. 11734) The present invention relates to a method of applying a plurality of separate coating materials to a support in layer relationship, and particularly to a method of applying all of the coating materials simultaneously while maintaining a distinct relationship between the different layers after they have been cured or dried on said support.

There are many instances in the coating art where it is necessary to apply two or more layers of coating materials, one on top of the other, so that the final product consists of a support having a plurality of distinct layers of the coating materials on one surface thereof. Depending upon the article involved, the different layers of coating will have different individual functions in the final product and it is, therefore, necessary that the individual coatings remain distinct from one another, i. e. that one layer not contaminate nor mix with the adjacent layer and that each layer have a given thickness which may or may not be the same as the thickness of any of the other layers.

A classic example of such a multiply coated support is found in the manufacture of photographic films and papers. A simple photographic film may consist of a support of some cellulose derivative, i. e. cellulose acetate, which has coated on one surface thereof a lightsensitive emulsion and on top of that a coating of some transparent material whose function it is to protect the emulsion from abrasion. Such a film may also have a thin subcoat of some material applied to it before emulsion coating in order to facilitate spreading of the emulsion thereon and to increase its tenacity with the support. When one considers the colors sensitive photographic films, then there are several individual coatings which must be applied. There may be the subcoating, a blue sensitive emulsion, a red-sensitive emulsion, a green-sensitive emulsion, a protective coating, one or more color filtering coatings, etc.

The customary manner of applying multiple layers of coating materials to supports has been to apply each each layer before the subsequent one is applied. Such .a procedure has been slow and expensive since it involves much time and the duplication of coating and drying equipment. In an effort to cut down on the expense of such multiple coating, I am aware that one coating has been laid down upon a second coating after it has been applied but it is still fluid, the advantage of such method being that it cuts down on the drying equipment needed by allowing the two coatings to be dried at the same time. I am also aware that in order to obtain a final thickness of a certain coating on a support, it has been suggested that a plurality of thin coatings be successively applied to the support to build up to the desired final thickness, such technique being used to overcome certain problems encountered in drying a single coating of the desired thickness and maintaining the neces sary uniform thickness and a flat surface. This lastmentioned coating technique is not analogous to the.

present invention since each layer is identical and contamination or mixing between layers is not a factor. Or, stating it another Way, there is no necessity for keeping the individual layers distinct from one another.

One object of the present invention is to provide a method of applying a plurality of separate coating materials to a support simultaneously and still maintain a distinct relationship between the different layers.

Another object is to provide a method of coating a support with a plurality of coating materials simultaneously and curing or drying all of said layers at the-same time while still maintaining a distinct layer relationship between the coatings.

A further object is to provide a method of coating as described which involves the customary bead method of coating, but in which the several coating materials are simultaneously fed into said bead and are coated therefrom in the desired layer relationship.

And still' a further object is to provide a method of coating as described wherein the thickness of the individual layers is controlled by the rate at which the different coating materials are fed into the coating bead.

And another object of the present invention is to provide a method of coating a plurality of colloidal-materials onto a support in distinct layer relationship which comprises simultaneously applying each of the colloidal materials in solution form onto the support at the same point.

And still another object is to provide a method of coating a support in the manufacture of photographic film and/or paper which comprises simultaneously applying one or more light-sensitive emulsions, and/ or subcoatings, protecting layers and light filtering layers to the support at the same time and maintaining a distinct layer relationship as well as a desired thickness regulation of each layer.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its mode of operation, together with additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawings, in which:

Fig. 1 is a schematic, part side elevational, part sectional, view of'a form of apparatus including a dual hopper which may be used to simultaneously apply two layers of coating material to a web in accordance with the present invention;

Fig. 2 is an enlarged sectional view of just the dual hopper used in connection with the apparatus of Fig. 1;

Fig. 3 is a greatly enlarged fragmentary section of the dual hopper shown in Fig. 2 and illustrating how two layers of coating material are simultaneously applied to the surface of a web;

Fig. 4 is a fragmentary section showing a color photographic film coated with four difierent layers of material and using a dual hopper;

Fig. 5 is an enlarged fragmentary section of a triple hopper by the use of which three layers of coating material may be applied to a surface of a web in accordance with the present invention;

Fig. 6 is a front elevational view of a multiple hopper which can be used to simultaneously apply four coatings to the surface of a web in accordance with the present invention;

Fig. 7 is a partial top plan view of the multiple hopper shown in Fig. 6;

Fig. 8 is a sectional view taken substantially on line 88 of Fig. 6;

Fig. 8A is an enlarged detail of Fig. 8 showing how' 5 into the coating bead by the hopper;

v Fig. 9 is a "sectional view of a dual slide hopper by. means of which'two layers of coating material may be simultaneously applied to the surface of a web in accordance with thepresent invention;

Fig. l0 is a sectional view-of :a multiple slide lhopper b y .the use of which four layers of coating. material may be applied to the. surface of a web simultaneously in accordance with the .present invention;

Fig. 11 is-a sectional view showing a combined-extrusion and'slide hopper by means of which two layers of coating material may be simultaneously applied to a surface of a web in'accordance with 'thepresent invention; and V V a Fig-l2 is a sectional view showing --a combined-extrusion and slidehopper by means of whiehithreie layers of coating material may be appliedr-imaccordance with the :present invention.

As pointed out above, inthe manufacture of. supports or-continuous'webs which requireithe applicationoftwo or-more separate coatings in superposed.layer.relationship on one surface, it is the customaryprocedure toi'place each of qthe coatings; on the support-in successionsand tojsetand/or dry ,each coating before the aapplioation of the next. Such aprocedu're has been deemed necessary in order to maintain-a distinct-relationship between thewebiorsupport, a classic example, and one which will be used by way of-specific illustration in disclosing the present invention, is the manufacture --of light=sensitive products,-such a's photographic film and/or paper.

'Inthe manufacture of photographic -film and paper there'are usually at least two separate coatings-applied to *the surface of a support, and in the case of color sensitive products, this number of coatings runs as high as'eight or more.

emulsions, .eaeh ene sensitive to "a different Wave-length, light filtering l'ayers, subbing layers, 'a protective layer,

etc. "In the application of' certain of these layers, Kitriiaybe aeeessar that there be -rio'con'tamination ormixing at the interface and the thickne'ss'of thedifi'ercut-layers may be' fairlycritical. Likewise, the order=in which thelayers are applied to *the' supp'ort is important.

In' orderto satisfy all of these requirements, the customary'*p'r6cedureof applyingth'esecoatirigs has been to applythem one at'a time in succession "and' 'setting and drying each coating before applyingthe succeeding one. These coatingsare "usually {applied by putting the diflei'ent materials in solution and coating them in this form, by any number of difierent't'echn'iques; onto-a 'con-'' tinuously moving support. Onewell-known 'coa'tingtec'h niqiie' involves" the -u se" "of" a'h'opper to the mouthor lips bf which the solution'is "fed 'atf a tilted rate, depend ing upon the thickness of coating desired, and from which -e' fi oi-t'picks' up a layer' of 'coatingfrom ab'ead formed "between the hopper mouth or "slot and thesupport.

.The present invention is concerned with the discovery that' two' or inore'of'these coatings can be'app'lied to a support simultaneously and still maintain"a"di'stin ct relationship "between the layers. The" difiere'nt materials coated according to the present invention, althou'gh 'co'at'ed in' the form "of solutions, do'n'ot"'-show anymorecontamination or mixture 'at' the interface" ofthe lawman-an the same materials when' coatedin successiodbythe ens- Inthe case of color films -these separ'ate-coating's mayinclude three separate silver-halide avenger tomary technique which involves a .completesettingand drying of each coat before the next is applied. By this novel method of coating the desired individual thickness of each layer of coating material can be regulated to the same extent as when the coatings are applied separately. Furthermore, this method is particularly suitable for applying thin coatings, or coatings having a dry thickness of fro'm..'less than one micron to 105025 inch.

This phenomenon is not limited to the coating of difcoatings of a photographic film, since each of the separate coatings in such a product are essentially waterpermeable gelatin solutions difiering only in the silver salt, the dye, or other materials, suspended or dispersed therein. For .best results, of :course, his desirable {to include .a. coating .aid such 'as isaponi-n, an ialkylisnlfate,

etc., in the coating i compositions.

.eInits broadestaaspects this methodv of coating; involves putting the materials to becoated in solution and simuL;

' pluralityi ofzthe samewor different fluidr coating composi tionsrcan be applied to the surface :of. a web :or supp'ort. in distinct layer relationship by feeding a layer. of .each of the :compositions from .a suitable coating device and combining said layers in the proper orientation. prior -.to.

their being. simultaneouslyapplied to the web :or' support in such eombined relau'onship. Experimentshave shown. that bythis method of applyingzmultiple layers of coating compositions that there is substantially no morev contamination orzmixing between zthe separate layers at.their;interface thanthere would be if the usual technique were used. :aFurtherm'ore, itahas been shown.thatthisaphenomenon :is'; not .dependent upon the different coating compositions having incompatible characteristics, l-but holdsi-itrue:especiallywhen two-layersof the-same coat. a ing composition :are simultaneously 'applied to the .coat-.

ing support. .Thexbroad method of :multiplemoating-is not..idependent .upon x. the 1 use of any, particularJ-form: of

coatingtapparatususoglong.asiit permits the formation of each? ofzzthe' coating compositions "into i a layer of "dc-1 sired-zithickness-zand tthenapermitsythese layers to :be

brought into surface contact.;.in..the desired orientation andzto-yzbelifedito thexasurfa'ce of the support -l1--.Sl.lCl1 arcombined relationship. A coating technique .vhich has; been found particularly applicable -to :this :method .of

- coating is1thewso-called beadimethod-of coating since the combinedilayersz of :difierent coating composition can be fed.i-.into: the bead 1.=from.v a: suitable coating device-and then be zsimultaneouslypicked :upon the 'SlllfECGuOf-B. support' moved across =andtin:=contact'-with said: bead.

- The bead method of .iapplying icoatings :to 2, a: moving webs-is well known .in the: an and needs. little. explanation.

Normally-itinvolves thei-useofia COailng;-d6. V-iC,.-l.t e.-.- a.. hopperg from which the: coating solution isf-fed atesa:

known r'ate in the form of a Wide, .l-thin 'ribborrmntothe surface bf aweb moved across .thezexit-slotz' ofithencoat-- ing device spaced slightly from thercoating device sand backed up by some sort:of backing roll or;.guiding ;-surfac the" coating device, tendsto pile up orifiphddlefhontthat whiclr serves to hold the web smooth atqthiszpoinb 6 application. The layer of coating solutiondeaving the dating: device, instead 0f (:o'atirlg -directly ioutaontotheweb in a layer-having a'thickness zequal to thatzleaving- .5 side of the coating device from which the web departs. This pile up or puddle of coating solution extends completely across the width of the web being coated and is normally referred to as a bead of coating. An enlarged cross-section of a typical coating bead is shown at 17 in Fig. 3. It can thus be seen that with this bead coating technique the coating is not in fact deposited directly onto the web from the coating device, but the coating device merely maintains the coating bead and the web is coated therefrom. With the bead method of coating the thickness of the coating laid down on a web moved thereacross will be determined by the action of the bead and will vary with the speed of web movement, the rate of supply of the coating solution, etc., and will not necessarily be equal to the width of the exit slot of the coating device. Throughout this specification and the claims associated therewith, therefore, the term coating bead will be used to mean a puddle or pile up of coating solution maintained in bridging relation between the surface of a web to be coated and a coating device which is stationary relative to the head of coating and spaced transversely from the support and across and in contact with which the surface of a web is moved to be coated therefrom. By the same token, the term bead coating will refer to that method of coating a web where the surface thereof is moved across and in contact with a coating bead and takes up the coating therefrom.

In Figs. 1 and 2 there is shown an apparatus which was successfully used to prove that this principle of coating at least two layers simultaneously onto a support was sound. Here there is shown a dual-feed coating hopper 10 having an exit slot 11, the lips 12 of which are slightly spaced from the surface of a web W backed up by a roll 13 which may serve to continuously move the web past the hopper slot. One coating solution S is continuously fed into an upper inlet 14 by a suitable metering pump P Whereas the second coating solution S is continuously fed into the lower inlet 15 by a separate metering pump P, see Fig. 2. An adjustable baffle 16 divides the interior of the hopper into two separate cavities and serves to direct the two solutions in the form of thin layers L and L toward the hopper slot 11. The hopper was made of a transparent plastic material and differently colored coating solutions were used so that the behavior of the solutions could be watched and it was obvious that the layer L of solution S coming into the upper inlet was on top of the layer L of the solution S coming into the lower inlet throughout the entire length of the exit slot 11. When the combined layers of solutions reached the coating head 17 between the hopper lips and the web W, this distinct layer relationship was maintained in the bead, despite apparent deformation of the bead, and an enlarged cross-section of the coated web after being dried showed that the two layers were distinct, extremely free of contamination or mixing at their interface, and possessed a relative thickness comparable to the rate at which each solution was pumped into the hopper.

The hopper 10 may be provided with any suitable form of adjustable mount so that the position of its exit slot 11 relative to the surface of the web W being coated can be adjusted for the best coating procedure. To this end, the hopper is carried by a frame 18 provided with bearings 9 rotatably journalled on the axle 8 of the backing roll 13 to permit the mount to be swung concentrically of the backing roll 13 so that the position of the hopper as a whole may be shifted around said roll. The frame 18 is capable of being locked in any adjusted position by means of a clamping screw 7 engaging an arcuate slot 6 in the support 19. The hopper per se is pivoted to the frame 18 at 29 so that the angle of the exit slot 11 may be critically adjusted relative to the surface of the web to be coated by means of adjustment of screw 5. To permit adjustment of the hopper to and from the web W to vary the distance between the web and the ends of the hopper lips, the hopper is slidably mounted on the frame 18 and connected with an adjusting screw. 21. After the web W has been coated, it is necessary to, set and/ or dry the coatings applied thereto. In the manufacture of photographic film or paper the coatings ap-. plied may be of the type which are set by cooling prior Referring to Figs. 2 and 3, it will be seen that the coating composition S entering upper inlet 14 is formed into a layer upon passing between the end of the bathe 16 and the upper inclined wall 24 of the hopper. Likewise, the coating composition S entering the lower inlet 15 is formed into a layer upon passing between theend of this baflie 16 and the lower inclined wall 25 of the hopper. These two layers are then brought into surface contact just prior to, or upon, entering the exit slot 11 of the hopper and are then directed by this hopper in this combined relation into the coating head 17 wherein they maintain the desired distinct layer relationship, as indicated in Fig. 3, and from which bead the layers are simultaneously coated on the surface of the web inthe desired layer relationship. It is pointed out that the width of the exit slot 11 is not equal to the combined thickness of the layers of coating composition directed thereto, but is preferably equal to the thickness of one of said layers or may even be less than this. This means that the velocity of the combined layers L and L passingthrough the exit slot 11 must be greater than that of the individual layers as they approach the slot, i. e. double,

if the two layers are of equal thickness and the compositions of which the layers are formed are being pumped into the hopper at the same rate. It should be pointed out that it is not the width of this exit slot 11 or the width of the slots forming the individual layers which determine the final thickness of the layers as they are applied to the web. This final thickness (wet) will be determined by the bead action and will vary with the velocity of the web, the rate of supply of the coating compositions, the efliciency of the hopper structure, etc. The relative widths of the exit slot 11 and the slots forming the individual layers of the diiferent coating compositions must be such as to permit the proper amount of the different solutions to be fed to the bead as determined by the bead laydown, and the rate at which the difierent compositions are pumped will be determined by the relative thickness of the two layers desired on the web. For example, if the coating S applied is to be twice as thick as coating S, then the slot widths are not varied, but coating S is pumped into the hopper at a rate twice that of coating S.

Experiments have shown that the types of coating compositions which can be applied by this method, as well as the relative thicknesses of coatings, the speed of coating, the velocity of the coating composition, etc. are apparently without limit in a practical sense of the word. In one test ofthis disclosed dual-feed hopper a coarse grain silver bromoiodide emulsion was pumped intothe lower inlet 15 and a nondiffusing colored gelatin solu-. tion was pumped into the upper inlet 14. The emulsion was pumped into the hopper with a metering pump froma melt at 5.35 pounds per silver mole for a coverage of approximately square feet per silver mole. The colored gelatin was pumped into the hopper through the upper inlet 14 by a metering pump from a solution containing about seven percent dry gelatin. Both pumps were driven simultaneously with a commercial metering unit. Two coatings were made on a cellulose acetate support, one at twelve feet per minute and the other at eighteen feet per minute and in each case the two layers were simultaneouslyjset'and dried by conventional equipment. Enlarged fcIOSS-seCtiOns of "the dried"films-showed excelle'nt' separation of the gelatin *and light-sensitive emulsio'n layers, and indicated that the relative thickness of the two "coatings was directly proportional 'to "the-rate at which the different solutions were pumped into the hopper. Although the speed of-coating-in'oneinstance was SOpercent greated than in the'other, therewas-ndiridic'a'tion'that the speed-of coating had any adverse eifect on the-distinct 'layercharacteristics of 'the applied coatmgs.

-Inanother experiment thecolored-gelatin of the above experiment was replacedwith-a' seven percent clear gelatin solution and'pumped with a smaller pump. Here again cross-sections of the filmsshowed excellent separadoubt the gelatin and emulsion layers.

I'n order to determine whether this coating principle mi'ghflalso "be satisfactory for theapplication of lightsensitive emulsions .used in the manufacture of color print material, the'followingcoatings weremade on a cellulose acetate support using the dual-feed hopper of Figs. 1-3 and producing a coated product shown in Fig. 4. {A5 shown in 'Fig.-=4,- this coated product comprises asupportor web W of cellulose acetate having successive layersof a blue-sensitized silver chlorobromide emulsion- B, ared-sensitized silver chlorobromide emulsion R, a green sensitized silver chl'orobromide emulsion G and a clear gelatin layer C, in that order. Since onlya dualfeed-hopper was used, the first two emulsions R andB wereapplied simultaneously. and the .third emulsion andandwas coated .at the rate of 21.30 pounds per silver moleand 1.78 pounds per hundredsquare feet giving a coverage of 1200 square feet per silver mole. The greensensitized emulsion containing 5.6 percent gelatin and amagenta coupler and was coated at the rate of 17.1 pounds. persilver mole giving a coverage of 965 square feet per mole. And theclear gelatin which contained seven percent gelatin was coated at the rate of .89 pound of solution per hundred square feet.

Visual inspection of cross-section studies ofthese coatingsfshowed no greater contamination between the individual layers than for layers of the samernaterials applied'ione layer at a :time as in conventional practice. Inaaddition, photographic tests of this color print material coatedr with a dual-hopper showedas good :results as'the same material coated one layer at a time in the' conventional way.

"-Inorder to ascertain whether or not three coatings could be applied according to this coating principle, a triple feed hopper of the type shown in Fig. 5 was constructed. This hopper 26 has an'exit slot 30, the lips 32 of which are slightly spaced from the surface of a web Whacked by'a roll 13'which may serve to continuously move the web past thehopper slot as before. The coa ing' material S" which is to be the bottom layer L" was pumped into the lower inlet 33, the coating material S which-was to be the center layer L was fed into the intermediate inlet 34, and the coating material S which was to be the top layer L was fed into the top inlet 35. Thethree coating materials were then directed to ward the hopper exit slot '30 by layer forming slots 36, 37*and 38, respectively, andthe three layersformed uponpassage through these slots flowed in combined relation through said exit-slotiati in theproper striated relationship. In this case the width of the intermediate layer L"-'-will-'be less thanthat of the-outer layers because the average velocitytofthe middle layer, 'is'higherthan thef averagevelocity at theedges due to 'friction between" the outer'layers'a'nd the faces of the "exit'slot. "Thissn-iated relationship of the different layers"of' coating materials "is retained-inthe coating bead 17 between the hopper' lips' and the'web W'so that the three'ditferent coating materials aredeposited simultaneously onto the web :in the proper layer relationship as the web moves *acrossanddn contact'withthe bead. 'In-an' efiort to determine the exact form of the coating bead l7 and just'what' sort of paths the three sep'arate layers of coating composition assume in passing-through the bead,:several different techniques wereused, including' photography, direct visual inspection with 'a 5Xfimagnifier, etc., without much success. While it was possible .to' ascertain the general shape of the exterior of the bead, it was practically impossible to obtain-anaceuratedetermination of the. paths taken by the individual layers, even when 'difierently colored solutions-wereused,-=because at the'edge'of the bead the uppermost -layer-=*or layers tended to now down over the others and obscure aview of the separate layers. Accordingly, 'while it is impossible to accurately depict the relationship of 'the different layers of coating solutions during their'passa-ge throughthe head, I have shown in Fig. 5 what is believed to occurlinithis connection. It is believed that the uppermost layer of solution :piles up on the outside face'of the' upper lip :due to capillary attraction and/ or surface aten- I sion, that'the'fmiddle layer of solution passes through the bead with little deformation, and that the lower .layer of solution backs into and fills the space :between fthe endxof. the lower lip and the web W due to capillary attraction :and/ or surface tension as indicated in: Fig.25. It is knownithat the form of the bead, vand.probably-the pathiof thetindividual layers moving ftherethrough,nwill vary rather widely with the speed of coating, the 'viscosityof. the coating solutions and the efficiencyofrxthe hopper construction. Notwithsstanding the fact. that :this conception of the bead form, and the form of the individ ual layers passing. therethrough, :may. not be. correct, ill. has been..unquestionably proven by the inspection.- of magnified cross-sections of materials coated in this manner that the individual layers of different coating solutions pass through the, bead -in.a regulated manner-without mixing and that a multilayer material coated according to this technique shows no more mixing orcontamination between the layers than would be experienced by using the conventional coating techniques where reach material is laid down in succession with complete drying between laydowns.

This triple feed hopper was tested in makingithe'lfour layer experimental;color .print' coating described" above. In this experiment, the blue; red, and green-sensitive emulsionswere applied simultaneously .as superposed liquidlayers in .the order specified and at a'coating speed of approximately twelvefeet per minute. After coating, the emulsions were set and dried simultaneously :by means of apparatus substantially like that disclosedrin Fig. l, and the cleargelatin overcoatwas vappliedseparatelyandset and dried. A check coatingwastthen made of these same materials by coating eachmaterial individually in the conventional-manner. When-these two multilayer coatings were exposed to a series of neutral and colored step wedges and processed in a conventional'color developer, the photographic tests of the two appeared identical, the color quality of both coatings being excellent. This test indicated that there wasino' more mixing or contamination between the separate layers when they were applied simultaneouslythan when they were applied separately and this fact was further proven by 'visual inspectionof enlarged cross-sections of the two coatings.

Having found that two or three different; coating mate-,

face of the layers, the question arose to what, if any, is the limitation as to the number of different coatings which might be applied in accordance with this coating principle.

Accordingly, a four-tube, multifeed hopper of the type shown in Figs. 6-8 was constructed and it was determined that four different coating materials could be simultaneously applied to a web and still maintain a distinct layer relationship between the coatings. This hopper is composed of a top section 40 and a bottom section 41 which are held in assembled relation by two end plates 42 and 43 fastened to the top and bottom sections by bolts 44. The forward edges of each of the top and bottom sections are spaced from one another to provide an exit or discharge slot 45 which extends across the width of the hopper and whose width is defined by end plates 42 and 43. The bottom section 41 is provided with a recess or chamber 46 communicating with the exit slot of the hopper by a curved convex surface 47. This chamber is divided into four sections by three dams 48, 49 and 50 which extend entirely across the width of the hopper chamber 46. Each of these dams includes a concave curved surface 51 and a convex curved surface 52 which cooperate with one another in opposite pairs to form gradually restricted flow passages 53, 54, 55 and 56 which cause coating solutions pumped into the enlarged portions thereof to spread out across the hopper and to be forced in thin streams or layers toward the hopper discharge slot 45. The convex surfaces 52 and the front wall 47 of the hopper chamber 46 each terminate in a substantially fiat surface 57 or 58 which is spaced from the lower face of the upper hopper section 40 to form discharge slots 59, 60 and 61 for forming the separate coating compositions into layers of regulated thickness and which layers are directed to the discharge slot 45. In order to facilitate assembly and to regulate the thickness of the individual layers of the different coating compositions in the hopper, each of the dams 48, 49 and 50 is made adjustable by means of a pair of adjusting screws 62 and set screws 63. By adjustment of screws 62 the width of each of the discharge slots 59, 60 and 61 can be regulated to the desired extent, and after the desired adjustment has been made, the set screws 63 are adjusted to lock the dams in such positions. Each of the four flow passages has connected thereto a nipple 64 onto the end of which one of four feed tubes 65, 66, 67 or 68 may he slipped. Each of the four feed tubes is connected to a supply of a different coating solution and from which supply the coating solution can be pumped into the hopper by separate metering pumps P at rates commensurate with the thickness of the particular coating layers desired in the final laydown.

I have found that if four different coating solutions are fed into the hopper through feed tubes 65, 66, 67 and 68 that they will be formed into four layers which will pass through the exit slot 45 of the hopper in distinct layer relationship and will be so deposited on a web W providing the web is fed across and in contact with a head of the solutions into which the combined layers issuing from the lips of the discharge slot are constantly fed. If the web is moved in a counterclockwise direction, looking at Fig. 8, then the layer of coating solution entering feed tube 65 will be deposited directly on the web surface, that entering feed tube 66 will lie upon the layer of coating solution from tube 65, that entering feed tube 67 will be next and finally that entering feed tube 68 will be the outermost layer. No attempt has been made to show in Fig. 8 the flow of the four separate layers of different coating compositions onto the web because of the small scale of that figure. However, in the enlarged detail section of Fig. 8A, the manner in which the four separate layers of coating compositions pass through the extrusion slot of this four-tube hopper and into the coating head for subsequent pickup by the web is illustrated to the best of applicants knowledge. If the direction of the feed of the web W across the bead is reversed, then the relationship of the layers of coating solution will be reversed on the web. As pointed out above, the relative thicknesses of the individual layers of the difierent coating solutions deposited on the web W will depend not upon the width of the discharge slot formed by the several dams and the upper section of the hopper but will depend upon the rate at which the respective coating compositions are pumped into the hopper. I have found that the above-mentioned orientation of the different layers of coating solution will not be affected by the order in which the pumping of the different solutions into the hopper is started.

This four-tube multifeed hopper was tested and proved by making a multiple coating of black and clear gelatin on a web of photographic support in the following manner. For this test the black gelatin was prepared by dispersing 2450 grams of a 3.7 percent black gelatin con taining a metallic silver dispersion in 5500 grams of ten percent photographic gelatin plus 1070 cc. of distilled water. The clear gelatin coatings were made from a solution of 6810 grams of ten percent photographic gelatin plus 2850 cc. of distilled water. Twenty cc. per liter of a 7 /2 percent saponin solution were added to each coating solution to act as a coating aid.

The coatings were made by applying the black gelatin in the first and third layers and the clear gelatin in the second and fourth layers. With the hopper shown in Figs. 68, this meant feeding the black gelatin into feed tubes 65 and 67 and the clear gelatin into feed tubes 66 and 68 and running the web W in a counterclockwise direction as indicated. After these coatings were set and dried, a photomicrograph of a cross-section of the multiple coating showed that all of the coats applied satisfactorily and that each layer was oriented in the proper relation. Furthermore, there appeared to be no mixing or contamination of the individual layers.

Having proved that there is apparently no limit to the number of separate coatings which can be simultaneously applied to a support by this method of coating, 2. series of tests were made to determine what limits, if any, there might be to the type of coating solutions which could be simultaneously applied to a support by this coating principle and still maintain a desired distinct layer relationship between coatings.

Two polyvinyl alcohol solutions, one a polyvinyl alcohol light-sensitive emulsion and the other a clear polyvinyl alcohol solution, were prepared and coated on a polyvinyl alcohol subbed cellulose acetate support at approximately twelve t'eet per minute. The triple feed hopper shown in Fig. 5 was used in this test with one of the chambers blanked out so that only two layers could be coated simultaneonus'ly. The light-sensitive emulsion was a silver bromide emulsion in four percent polyvinyl alcohol at pH=6.0, containing 60 cc. 7 /2 percent saponin solution and 160 cc. four percent borax solution at pH=5 .5. The clear polyvinyl alcohol solution was a six percent clear polyvinyl alcohol solution containing 95 cc. 7 /2 percent saponin solution and 250 cc. four percent borax solution per pound of polyvinyl alcohol. The lightsensitive solution was coated directly on the support at 3.0 pounds per hundred square feet and this was overcoated with l.5pounds per hundred square feet with the clear polyvinyl alcohol solution. After coating, these layers of coating material were set at room temperature by fuming with ammonia as described in U. S. Patent No. 2,376,371. Cross-sections were made of this coating, and under the microscope two distinct layers were visible and no apparent mixing of the two layers appeared to have occurred.

Commercial polyvinyl alcohol is hydrolyzed polyvinyl acetate having approximately 5% acetate. It is readily dissolved in water at ordinary temperature and behaves I like a typical reversible colloid. Gelatin likewise is readily soluble in warm water and is a colloid. Accordingly, the experimental coatings made show that this principle otsnnulltaneously coatinglayersofseparate" coating materialsontcr a support is applicable=with colloidal material which can be; put into solution;

Another ertampleof a three-layer coatingwhich was made inaccordancewith thepresent inventionusing the triple-feed hopper shown in Fig. -is*as"follows: In this example, the'top coat consisted'ofa'seven'percent gelatin solution containing a yellow colloidal silver dispersion and 270'cc.'of a seven and one-half'percent'saponin solutionfperp'ound of gelatin. The middle coat consisted of a"'seven "percent' gelatin "solution containing 63 cc. of a seven and one-half percent 'saponin solution'per pound of :gelatin. 'The'bottom coat'consistedofa sevenand one=halfipercent gelatin solution containing ablack'metallic silver dispersion and 60 cc of a'seven and one=half percent saponinsolutionper.piound of gelatin. All three coatswere "appliedsimultaneously onto a clear'tellulcse acetatefsupport at a coverageof. 1178 pounds 'perhundred quare feet'for each layerand at a coating speedoftwelve feet penminute. Excellent separation of the layers'was obtained, as shown by photornicrographs of a cross section of this coated web. The saponin solution-had no fiect' on the phenomenon of the layers'maintaining desired distinct relationship during and after coating, but was introduced into the difierent coating compositions to increase the spreading characteristics thereof so that they would more readily spread and produce an even coating.

Tdfind out what effect the speed of coating might have on this principle of multiple coating, a coating was made using the same apparatus and coating compositions as set forth in the immediately preceding example, except that the coating speed was eighteen feet per minute ratherithan twelve feet per minute. it was evident from an inspection of a photomicrograph of a cross-sectionof the coated support after drying the coatings that excellent separation of the layers was also obtained at this coatingspeedan'd it differed from the first example only in'that each of the layers were approximately ,6 as thick aswhen coated "at twelve feet per minute.

'That this method of coating is'applicable to the. multilayer coating of colloidal materialsother than gelatin and polyvinyl alcohol is evidenced by the following example: The colloid used in this test was cellulose ether phth'alate comprising an ethyl cellulose, havingan 'ethoxyl'content of approximately 45 percent phthalylatedaccording to the method described in U. SLFatent 2,093,46210' give a cellulose etherphthalate having an"apparent phthalyl content of 16.8%. In this test thc'ethyl cellulosephthalate employed as a coating composition wasiin thefor'rnot its salt, such as ammonium'salt, which-is" water soluble and two layers of this material were applied, according to this invention, onto acellulose'acetate'support with a coverage'of L25 poundsper hundred square feet *and' at al coating speed of six feet per minute. The top layerwas coated'froma clear solution "ofcellulose "'ether'phthalate saltand the bottom layer contained one part of carbon dispersion (Aqua Blak, made 'by -BinneyGmith) to nine parts'of the cellulose ether phthalate. The .carbon dispersion'was' added to one of the coatingcompositions merely to show whether or not the two'materials coated in distinct layer relationship without contamination or mixing" at the interface of the layers. Photornicrographs of a' cross-section of the webso coated showed clearly that good separation of the layers was also obtained with these coating compositions.

The following example points out that it is possible-to simultaneously-coat two layers ofcoati-ng -composition in accordancewith the present invention -which are :not

colloidal materials and still obtain good separationbe 'tic les' in water. 'lhese coatingsi were applied with the triple'feed hopper shown 'in Fig. 5 "set up 'for dualr applh cation, thatis, the middle 'se'cticnwas'blocked ofiandihe coating solutions were applied only through thetopntrd bottom inlets. In order to obtain a polymeric'hydrosol for this test, a commercially available aqueous dispersion of'an acrylate're'sin sold under the trade-name Rhoplex wasused. :Rhoplex'is manufactured by Rohm '& Haas and is believed .to 'be an acrylate acrylonitrlle polymeric hydrosol formed by the emulsion polym'erization of an acrylate'and acrylonitrile in water. The top coatwas made of clear Rhoplex whereas the bottom layer was made of Rhoplexito which was added an aqueous dispersion of carbon particles merely to show the separation of the two layers. Both layers were coatedat a coverage of 1125 pounds per hundred square feet and at arate ofsix feet per minute. Afterthese layers were deposited on' the support, the water was evaporated whereupon the particles of the polymeric hydrosol coalesced and formed continuous layers of the pdlymer. 'A photornicrograph of the dried coating showed excellent separation between the clear and black layers of-polymers depositedon the web.

This novel method of multiple coating a web isnot limited to the use of extrusion type hoppers alreadydisclosed, but can be successively carried out, even with certain advantages, with other types ofcoating devices.

This method of coating may be readily carried out by the use of a multiple slioehopper of'the type'disclosed in jcopending US. application Serial No. 489,969,.filed on even date herewith in the names. of MercierQT-l-orpey and Russell. In'Fig. 9 there is shown a double slide hopper by the use of which adu'al coating may be made in accordance with the present invention. With this hopper, one 'fiuid coating composition '74 is continuously pumped by a metering pump'P into a cavity '75 at a given rate throu'gti.inlet 7otandflfrom which itis'torced through a narrow vertical .slot77 .in.the term of a ribbon and out onto a downwardly inclined slide surface"-78 down which it 'flows by gravity in the form of a'layer"79 'to a point where it forms a coating head 17 between the end of the slide surface anda web' W moved upwardly across and in contact Withfthe' beadby .a supporting roll 13. The second coating composition 80 is continuously pumpedinto a second cavity 31 at a ,given rate by another'meteringpump'P through inlet 82 and from which it is forced through a narrow vertical slide83 in'the form of a ribbon and onto a second-downwardly inclined slide surface8 4. Thishribbon of the second coatingcomposh tion inifiowingdown the slide. surface 84 under the influenceof gravity forms aismoo'th,'uniformly'thiclnlayer 85. The twouslide. sni-faces '78iand 84 are co'planar, or substantially so, so .thatas the layer-"diofthe second coatingcomposition reaches the ribbon of thefirst coating composition .being extruded through slot7"7, it"flows up -ontop of..the sarneoand the two then flow -to-' gether. downslide surfaceVS and into the coating head 17. The :relative thickness oftthe two layers of coating material will depend upon the rate .at which they are pumped into-their .respectivetcavities Hand 81. ".The hopper .is provided withu-pipes 85 through which hot .or cold =fiu-ids can :beci-rculated toekeepethe coating composition-ina-desired fluidstate.

\Usinga .doubleslide :hopper-ofzthis type, .a gelatino silver halide photographiceemulsion.and a; protective coat of clear gelatin :rhave -beenasimultaneously coated onto a baryta-coated paper-40 ainchesrwidetat aspeed of .100 feet per minute to produce. ta. commercial photographic paper havingiias;,goodicharacteristicsas the sameproduct having the two coatings applied successively and with-a completeidrying. of :the emulsiont'coat prior to; application of the protective gelatin coat. To obtainoptimum conditions at::this coatingt speed, it :was -found desirable .to useiatvacuum ion the .=bead,-..asl is described in .U. .SiPatent 2,681,294. This. example clearly shows; that .this .method of; coating :issnot-limitedto. the coating .of narrow .Width sheetskandzat slow coatingi speeds; but isequally adapted for the coating of commercial width product at high coating speeds.

In Fig. there is shown a l our slide hopper by the use of which four separate layers of the same or different coating compositions can be simultaneously applied to the surface of a web in accordance with the present invention. In this device the first coating composition is continuously pumped at a given rate into a cavity 90 from which it is extruded through a narrow vertical slot 91 out onto a downwardly inclined slide surface 92 over which it flows by gravity to form a layer of that compo-sition. Likewise other coating compositions are continuously pumped into chambers 93, 94 and 95 and are extruded from narrow vertical slots 96, 97 and 98 respectively onto slide surfaces 99, 100 and 101, respectively, down which they flow by gravity to form separate layers of the different compositions. The four slide surfaces are coplanar so that as the layers of difierent coating compositions flow down their respective slide surfaces they are brought together in overlapping relation and by the time the four layers reach the coating head 17 they are combined in the desired laminated relationship. This distinct layer relationship is maintained throughout the bead so that as the Web W is moved across and in contact with the head, it takes up on its surface the four layers of coating in the desired orientation and with the layers being distinctly separate from one another and of a relative thickness commensurate with the rate at which each was pumped into the hopper. So far as I have been able to ascertain, there is no limit as to the number of separate layers of coating compositions which can be laid down on a Web with a multiple slide hopper of this type.

This method of multiple layer coating is not limited to the use of hoppers of the extrusion type or of the slide hopper type but is equally adapted to the use of a combination of these two types of hoppers which are disclosed in copending U. S. application Serial No. 489,864, filed on even date herewith in the names of Wilson, Sanford and Russell.

In Fig. 11 a hopper is shown which combines a single slide hopper with a single extrusion hopper in accordance with the Wilson et al. disclosure. In this device one fluid coating composition X is continuously pumped into a chamber 110 and is extruded therefrom as a layer 111 from a substantially horizontal extrusion slot 112 directly toward the coating bead 17 across and in contact with which the web W is moved in the direction of the arrow while passing around roll 13. The other coating composition Y is continuously pumped into chamber 113 at a given rate and is extruded as a ribbon through substantially horizontal slot 114 onto a downwardly inclined surface 115. As this ribbon of solution flows down the slide surface 115 by gravity, it is formed into a layer 116 of desired thickness and is brought into surface contact with the layer 111 of the other coating composition at the time it leaves extrusion slot 112 so that they move into the coating bead in combined relation. In accordance with the present invention, these two layers of coating composition are picked up by the Web W and appear on the web, after drying, as two separate and distinct layers oriented so that the layer 111 extruded through slot 112 lies directly on the surface of the web and the layer 116 formed on the slide surface lies on top of layer 111.

In Fig. 12 a hopper is shown which combines a single slide hopper with two extrusion hoppers in accordance with the Wilson et al. disclosure, and by the use of which a triple coating can be made on a web in accordance with thepresent invention. In this device one coating solution Z is continuously pumped into a chamber 120 and is extruded as a layer 121 from an upwardly inclined slot 122 directly toward the coating bead 17" across and in contact with which the surface of a web W is moved in the direction of the arrow while passing around backing roll 13. A second coating solution Z' is continuously pumped into chamber 123 at a known rate and is extruded as a layer 124 from a substantially horizontal slot 125 directly toward the coating head. The third coating solution Z" is continuously pumped at a known rate into chamber 126 and is extruded as a ribbon through a substantially horizontal slot 127 onto a downwardly inclined slide surface 128. As this ribbon of solution flows down the slide surface 121, it is formed into a layer 129 of desired thickness and smoothness. It will be observed that the extrusion slots 122 and 125, and the lower end of the slide surface 128, are so disposed that the three layers of coating solution formed individually thereby or thereon, as the case may be, are brought together in surface contact with one another just prior to the three layers entering the coating bead and prior to being applied to the web. The three layers thus pass into the bead and are coated out on the web in distinct and separate layer relationship and are so oriented that the layer of coating solution Z is adjacent the web, the layer of coating solution Z is directly on the layer of coating solution Z, and the layer of coating solution Z" is the outermost of the three and in surface contact with the layer of coating solution Z. A feature which distinguishes this form of hopper from the dual extrusion hopper shown in Figs. 2 and 3 is that each hopper charnber has its own extrusion or distributing slot (122 and 125) so that the layers of the individual coating solutions do not meet until after passing from the slots. This shows that the present method of multiple coating is not limited to forming and bringing the individual layers together a substantial period of time before they are introduced into the coating bead, but that the individual layers can be combined just prior to, or at the time, they enter the bead and the desirable results of obtaining a multiple layer application with distinct layer relationship will still be achieved. These combined slide and extrusion hoppers have been successfully used to simultaneously apply different types of commercially used gelatino silver halide light-sensitive emulsions and protective coats of gelatin, and to simultaneously coat the light-sensitive color emulsions used in the making of color photographic films mentionedabove in discussing the dual and triple extrusion hoppers shown in Figs. 3 and 5. In each instance the product multiply coated With this method was as good in all respects, both physical and chemical, as a product coated in the conventional way by applying the different coatings successively with complete drying between each coating. These hoppers have been successfully used to coat webs 44% inches wide at speeds of coating ranging all the way from 24 feet per minute to feet per minute.

I am unable to explain why two or more layers of coating composition when simultaneously coated onto a web in accordance with the present invention do not mix but maintain a layer relationship as distinct and as free of mixing and contamination at the interface of the layers as when the same compositions are coated successively with a complete drying of each coating before the next one is applied thereto. It is not based on the fact that the difierent coating compositions are physically or chemically non-compatible because, as the example show, the same results were obtained when all of the coating compositions Were' identical both physically and chemically, except that a dye or carbon dispersion was incorporated in one to give visible proof of this phenomenon.

In attempting to explain the reason why the different layers of coating composition do not mix when coated according to the present invention, the question of whether it was because a form of liquid motion known as laminar flow was involved as distinguished from a form of motion known as turbulent flow has been considered. Ac cording to the Reynolds theory of fluid motion (R. C. Binder, Fluid Mechanics, Prentice Hall, 1943, p. 71), when two separate streams of water are passed through a pipe, they will stay separated due to a condition of laminar flow so long as the critical velocity is not reached andafter' the critical-velocity isreach'ed, the flow becomes turbulent and the streams will 'mix. *Reynolds showed that the 'criticalvelocity dependedon the diameter 'of the pipe, 'the velocity of the fluids' 'passing throughthe pipe, itsdensity, and its viscosity, and that if'thesefour factors were combined in one way, andone way only, a function known as the Reynolds number would be obtained giving the critical velocity for 'the flow of a fluid through'a pipe. While this theory might be applied to explain the reason Why the separate layers do not mix in'passing in combinedre'lation throughthe exit slot in one of the disclosed extrusion type hoppers, on the basis that the flow is laminar because'the-Reynolds'number is not high enough to reach thecritical velocity, it does not s'eem'to apply when the multiple slide-hopper or combined slide and extrusion hopper techniquesare used, nor does it explain the maintained 'separationof the layers through the coating bead 'andja'fter disposition on the Web until they are dried, because thelayersare not moving through a. pipe nor are they totallyconfin'ed-in any way. The one explanation for this phenomenon which -might'be advanced is that normallyit'takes an appreciable time for two solutions to mix even if they are brought together in such a Way as to provoke turbulence, and with applicants method of coating-the different-layers are not in combined layer relationship long enough, before being deposited on the'web, to allow noticeable mixing to take place even if the conditions of flow are such as to be conducive to such a'mixing. As to why the layers 'of coatingmaintainiheir separate relationship between the time they are depositedon' the web and they are completely dried is inexplainableexceptdn the caseof those coating compositions which are capable of being set'by chilling, heating, or by chemical action immediately'after deposition on'the webisurface and prior to drying. Here again the elementof time might be the critical factor since thev time elapsing between the deposition of the layers on the web and the time 'thecoating is dried is relatively shortv and perhaps less'than the time required for the coatings, or the materials dispersed therein, to diifuse into one another.

As pointed out above, in the manufacture of photographic films involving the application of protein coatings from aqueous solutions thereof, the coating at the tllIlEDf application is in liquid condition, and in order to accomplish drying of that coating,it may be desirable that ltfirst be set. One way of doingthis is chemically, as taught by U. S. Patent 2,652,345, which teaches adding an. aldehyde to thecoating solution and 'then fuming the same after coating with gaseous ammonia to rapidly-set the coating.

Ihave found thatlmy'novel method of multiple coating makes it possible to carry out this-idea of chemically settmg such coating solutions in a more direct and convenient manner without the need for the use of-ammonia in gaseous form and without the problem incident to subjecting a freshly coated web to such a gaseous treatment without the danger of roughingthesurface cf the coating due to the injection of gas underpressure' onto such-a fresh coating. With the present method of coating, if two different protein coatingsolutions are being applied to a support andan aldehyde, e. g. formaldehyde, is introduced into one and1ammonia is introduced into the other, then when the two-layers come together at the time of coating the ammonia and formaldehyde presumably diffuse throughout both layers causing them to set simultaneously.

The following coatings were made and showed this chemicalsetting tookplace without in any way affecting' the distinct layer relationship of the two'coatings laid doWnon-the Support. Two coating solutions (1) a silver bromoiodide emulsion containing 60 cc. 7% saponin'and 20 cc. of l% formaldehyde per silver mole at pH=6.'0 and 7% dry; gelatin 'and.(2) a7% clearzgelatin-solution containing 60 cc. '7 /2%' saponin and sufiicient amountof NI-LiOH to raise the pH 'to 8 were first simultaneously coated by the use of the dual hopper shown in"Fig.'2 "'at approximately 12 feet per minutewith'the emulsion directly on an acetate support. The emulsion was coated at a rate of 3.0 lbs./ square feet and the gelatin solution Was'coated at a rate of 1.5 lbs./ 100 square feet on 'top of the emulsion layer. In another run the same materials were coated the same as in the first run but with the layers reversed, i. e. withthe emulsion on the wet gelatin layer. In a third run the two materials were coated the same as in the first run but with the gelatin solution at pH:9.0. All of these experiments gave good separation of the two layers even though the formaldehyd and ammoniadiffused freely between the two layers to chemically set them in very short order.

While I have shown and described certain specific embodiments of myinve'ntion, I am aware that many modifications thereof are possible. My invention, therefore, is not to be limited to the precise details shown and described but is intended 'to cover'all modifications coming within the scope of the appended claims.

Having'thus described'rny invention,'what I claim is new and desire to secure by Letters Patent of the United States is:

1. The method of simultaneously applying thin coatings of a plurality of colloi'dalmaterials onto a Web support in distinct layer relationship comprising the steps of making a solution of each of said colloidal materials, forming a coating head of said solutions in bridging relation between the surfaceof the support and a stationary coating device spaced transversely therefrom, simultaneously feeding each of said solutions in the form of a layer into said head and in superposed relation to'i'the other solutions whereby "the individual layers are maintained in distinct superposed relation, and continuously moving the surface of said support across and in contact with said bead so that the surface of the support engages one of the outermost of the superposed layers in said head and simultaneously picks up all of said layers and moves away from the head with the solutions in distinct superposed layers.

2. The method ofsimultaneously applying thin coatings of a plurality of colloidal material's onto a web support in distinct layer relationship comprising the steps of making a solution of each of said colloidal materials, forming a coating bead of said solutions in bridging relation between the surface of the support and 'a stationary coating device spaced transversely therefrom, simultaneously feeding each of said solutions in the form of a layer into said bead and in superposed relation to the other solutions whereby the individual layers areimaintained in distinct superposed relation,-and regulating the relative rate of flow of said solutions into said beadcommensurate with the relative thickness of the layers ofv each material desired on said support, and continuously moving the surface of said support across and incontactwith said head so that the surface of the support engages one of the outermost of the superposed layers in said head and simultaneously picks-up all of said layersand moves away from the bead with the solutions in distinct superposed layers having a thickness varying in direct proportion to the rate at which the individual solutions are fed into saidbead.

3. The method of simultaneously-applying thin coatings of a plurality of gelatin solutions onto a web support in distinct layerrelationship comprising the steps of-forming a coating beadof said'solutionsin bridging'rela'tion between the surface of the support and a stationary coating device spaced transverselytherefrom, simultaneously feeding each of said solutions-in the formof allayerinto said head and in superposed relation. to the other solutions whereby the individual layers are maintained in distinct superposed relation; and continuously moving the surface.

of said'support across andincontact withsaid head so that the surface ofthe support engages oneof the outermost of the superposed layersin-said bead'and simulta- .17 neously picks up all of said layers and moves away from the bead with the solutions in distinct superposed layers.

4. The method of simultaneously applying thin coatings of a plurality of polyvinyl alcohol solutions onto a web support in distinct layer relationship comprising the steps of forming a coating head of said solutions in bridging relation between the surface of the support and a stationary coating device spaced transversely therefrom, simultaneously feeding each of said solutions in the form of a layer into said bead and in superposed relation to the other solutions whereby the individual layers are maintained in distinct superposed relation, and continuously moving the surface of said support across and in contact with said bead so that the surface of the support engages one of the outermost of the superposed layers and moves away from the head with the solutions in distinct superposed layers.

5. The method of simultaneously applying thin coatings of a plurality of gelatin and polyvinyl alcohol solutions onto a web support in distinct layer relationship comprising the steps of forming a coating head of said solutions in bridging relation between the surface of the support and a stationary coating device spaced transversely therefrom, simultaneously feeding each of said solutions in the form of a layer into said head and in superposed relation to the other solutions whereby the individual layers are maintained in distinct superposed relation, and continuously moving the surface of said support across and in contact with said head so that the surface of the support engages one of the outermost of the superposed layers in said bead and simultaneously picks up all of said layers and moves away from the head with the solutions in distinct superposed layers.

6. The method of simultaneously applying thin coatings of a plurality of liquid gelatino silver halide emulsions onto a web support in distinct layer relationship comprising the steps of forming a coating bead of said emulsions in bridging relation between the surface of the support and a stationary coating device spaced transversely therefrom, simultaneously feeding each of said emulsions in the form of a layer into said head and in superposed relation to the other emulsions whereby the individual layers are maintained in distinct superposed relation, and continuously moving the surface of said support across and in contact with said bead so that the surface of the support engages one of the outermost of the superposed layers in said bead and simultaneously picks up all of said layers and moves away from the head with the emulsions in distinct superposed layers.

7. The method of simultaneously coating a gelatin solution and a liquid gelatino silver halide emulsion onto a web support in distinct layer relationship comprising the steps of forming a coating head of said solution and emulsion in bridging relation between the surface of the support and a stationary coating device spaced transversely therefrom, simultaneously feeding each of said gelatin solution and said emulsion in the form of a layer into said bead and in superposed relation with each other whereby the individual layers are maintained in distinct superposed relation, and continuously moving the surface of said support across and in contact with said bead so that the surface of the support engages one of the superposed layers in said head and simultaneously picks up each of said layers and moves away from the bead with the gelatin solution and gelatino silver halide emulsion in distinct superposed layers.

8. The method of simultaneously applying thin coatings of a plurality of polyvinyl alcohol silver halide solutions onto a web support in distinct layer relationship comprising the steps of forming a coating head of said solutions in bridging relation between the surface of the support and a stationary coating device spaced transversely therefrom, simultaneously feeding each of said solutions in the form of a layer into said head and in superposed relation to the other solutions whereby the individual layers are maintained in distinct superposed relation, and continuously moving the surface of said support across and in contact'with said head so that the surface of the support engages one of the outermost of the superposed layers in said head and simultaneously picks up all of said layers and moves away from the head with the solutions in distinct superposed layers.

9. The method of simultaneously coating a liquid gelatino and polyvinyl alcohol silver halide emulsions onto a Web in distinct layer relationship comprising the steps of forming a coating bead of said liquid gelatino and said emulsions in bridging relation between the surface of the support and a stationary coating device spaced transversely therefrom, simultaneously feeding each of said liquid gelatino and said polyvinyl alcohol silver halide emulsions in the form of a layer into said head and in superposed relation with each other whereby the individual layers are maintained in distinct superposed relation, and continuously moving the surface of said support across and in contact with said head so that the surface of the support engages one of the outermost of the superposed. layers in said head and simultaneously picks up each of said layers and moves away from the bead with the liquid gelatino and polyvinyl alcohol silver halide emulsions in distinct superposed layers.

10. The method of simultaneously applying thin coatings of a plurality of like colloidal materials onto a web support in distinct layer relationship comprising the steps of making a solution of each of said colloidal materials, forming a coating bead of said solutions in bridging relation between the surface of the support and a coating device which is stationary relative to said bead and spaced transversely from said support, simultaneously feeding each of said solutions in the form of a layer into said bead and in superposed relation to the other solutions whereby the individual layers are maintained in distinct superposed relation, and producing a continuous relative movement between the bead and the surface of said support whereby the support moves across and in contact with said head and one surface of the support engages one of the outermost of the superposed layers in said bead and simultaneously picks up all of said layers and moves away from said head with the solutions in distinct superposed layers.

11. The method of simultaneously applying thin coatings of a plurality of difierent colloidal materials onto a web support in distinct layer relationship comprising the steps of making a solution of each of said colloidal materials, forming a coating bead of said solutions in bridging relation between the surface of the support and a coating device which is stationary relative to said head and spaced transversely from said support, simultaneously feeding each of said solutions in the form of a layer into said bead and in superposed relation .to the other solutions whereby the individual layers are maintained in distinct superposed relation, and producing a continuous relative movement between the bead and the surface of said support whereby the support moves across and in contact with said head and one surface of the support engages one of the outermost of the superposed layers in said bead and simultaneously picks up all of said layers and moves away from said bead with the solutions in distinct superposed layers.

12. The method of simultaneously applying thin coatings of a plurality of settable colloidal materials onto the surface of a flexible web support in distinct layer relationship comprising the steps of making a solution of each of said colloidal materials, forming a coating bead of said solutions in bridging relation between the surface of the support and a stationary coating device spaced transversely therefrom, simultaneously feeding each of said solutions in the form of a layer into said bead and in superposed relation to the other solutions whereby the individual layers are maintained in distinct superposed relation, continuously moving the surface of said 19 support across and in contact with said head so that the surface of the support engages one of the outermost of the superposed layers in said bead and simultaneously picks up all of said layers and moves away from the bead with the solutions in distinct superposed layers, and

setting the deposited layers of said solution to prevent them from flowing relative to "each other and said support.

13. The method of simultaneously applying thin c'oatings of a plurality of aqueous gelatin solutions onto the surface of a flexible webysupport in distinct layer relationship comprising the steps forming a coating bead of said solutions in bridging relation between the surface of the support and a stationary coating device spaced transversely therefrom, simultaneously feeding each of 7 said solutions in the form of a layer into said head and in superposed relation to the other solutions whereby the individual layers are maintained in distinct superposed relation, continuously moving the surface of said support across and in contact with said bead so that the surface of the support engages one of the outermost of the superposed layers in said head and simultaneously picks up all of said layers and moves away from the bead with the solutions in distinct superposed layers whose indithe suffaceo'f a flexible webfsuppoft in distinct layer relationshi :comprisin'gfthe' steps forming a coating bead of said solutions in "giug 7 re jation 'b'etweenifthe surface of the, support "and "a stationary ebating device'spaced transversely therefrom, simultaneously feeding each of said solutionsjin the'form of a 'layefintosaid bead and in superposed relation't'o the othe'rsolutions whereby the V individual layers are maintained in' distinct superposed relation, continuously moving the surface of said "support 'across and in contact wtih said bead so that the surface of the support engages one of the outermost of the superposed layers in said head and simultaneously picks up all of said 'layers'and moves away from the head with the solutions in distinct superposed layers whose individual relative thicknesses depend upon the rate at which each solution is fed into 't h'e' bead and whosecbmbined thickness depends upon the speed-of "the support, and simultaneously drying said deposited layers of solution.

vidual relative thicknesses depend upon the rate at which each solution is fed into the bead and whose combined thickness depends upon the speed of the support, setting said layers of deposited solutions to prevent flow thereof relative to the support, and then simultaneously drying the water from said deposited layers of solution.

14. The method of simultaneously applying thin coatings of a plurality of polyvinyl alcohol solutions onto Asbeck "a Dec. 13, 1955 

1. THE METHOD OF SIMULTANEOUSLY APPLYING THIN COATINGS OF A PLURALITY OF COLLOIDAL MATERIALS ONTO A WEB SUPPORT IN DISTINCT LAYER RELATIONSHIP COMPRISING THE STEPS OF MAKING A SOLUTION OF EACH OF SAID COLLOIDAL MATERIALS, FORMING A COATING BEAD OF SAID SOLUTIONS IN BRIDGING RELATION BETWEEN THE SURFACE OF THE SUPPORT AND A STATIONARY COATING DEVICE SPACED TRANSVERSELY THEREFROM, SIMULTANEOUSLY FEEDING EACH OF SAID SOLUTIONS IN THE FORM OF A LAYER INTO SAID BEAD AND IN SUPERPOSED RELATION TO THE OTHER SOLUTIONS WHEREBY THE INDIVIDUAL LAYERS ARE MAINTAINED IN DISTINCT SUPERPOSED RELATION, AND CONTINUOUSLY MOVING THE SURFACE OF SAID SUPPORT ACROSS AND IN CONTACT WITH SAID BEAD SO THAT THE SURFACE OF THE SUPPORT ENGAGES ONE OF THE OUTERMOST OF THE SUPERPOSED LAYERS IN SAID BEAD AND SIMULTANEOUSLY PICKS UP ALL OF SAID LAYERS AND MOVES AWAY FROM THE BEAD WITH THE SOLUTIONS IN DISTINCT SUPERPOSED LAYERS. 